The use of a solvent, miscible with a (lower) alkyl ketone peroxide and exhibiting a boiling point of between approximately 185 and 225° C., for thermally stabilizing organic peroxide has been disclosed in the document FR 1 594 180. This document teaches that the solvent is chosen from esters, aldehydes, ketones, hydrocarbons, halogenated hydrocarbons and epoxides. It also teaches that, in addition to the heat-desensitizing solvent, pyrrolidine stabilizers can be used to render the ketone peroxides stable on storage.
French Application FR 2 792 321 discloses a process for the manufacture of a controlled-rheology resin from a homopropylene or propylene copolymer in which, in place of the peroxides of the state of the art or in addition to the latter, stable free radicals, such as nitroxides, are incorporated in the resin to be modified, introduced, for example, into the molten zone of an extruder.
Nitroxyl radicals are highly stable radical entities having an N—O functional group. Reference may be made to the publication by D. Griller and K. Ingold in Accounts of Chemical Research, 1976, 9, 13–19, or to that by A. Forrester et al. “Organic Chemistry of Stable Free Radicals” in Academic Press, 1968, for the definition.
These radicals have the property of reacting very rapidly with carbonaceous radicals resulting from the decomposition of initiators or resulting from radical processes, such as radical polymerizations. This reactivity has been taken advantage of by incorporating these nitroxyl radicals in radical polymerization processes, such as the polymerization of styrene or acrylates, or processes for the copolymerization, decomposition or modification of polypropylene.
The Applicant Company has just found that nitroxyl radicals can thermally stabilize peroxides and make it possible optionally to increase the stability of the latter on storage.